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Old 01-27-2013, 03:37 AM   #35
_cy_
Beastly Adventurer
 
Joined: Sep 2011
Location: Tulsa, Oklahoma
Oddometer: 4,480
Quote:
Originally Posted by Twilight Error View Post
I used to build LiIon batteries for the aerospace market. I would not install any one of the current crop of commercial LiIon batteries into my bike. The charging systems we've got are designed around Lead-Acid, which are vastly more tolerant of abuse than any LiIon chemistry available. Even the relatively forgiving Iron Phosphate variants don't match up well with our charging systems. I would wait until batteries with dedicated charge control electronics positioned between the charging system and the cells are on the market.
your comments may be true for the lithium cobalt based li-ion batteries. but you are way off on LiFePO4 not matching up with 12v motorcycle systems.

you know this but LOTS of other folks are getting confused with li-ion label which includes lithium cobalt used in Boeing 787 and lithium iron phosphate (LiFePO44) used in motorcycles. Lithium cobalt batteries are inherently unsafe ... overcharge by 1/2 volt over 4.2v full charge ... battery could go into thermal runaway (explosion) vs LiFePO4 has to subjected to wild abuse before it will finally catch on fire. LiFePO4 batteries are inherently stable and are the safest of all li-ion batteries.

think in terms of cell multiples... lithium cobalt based batteries operates at about 3.7v nominal, which mean that cell operates between 3.5v-4.2v fully charged. lithium cobalt based cells simply don't match 12v systems. compared to LiFePO4's 3.3v nominal which matches up nicely with 12v systems. LiFePO4 are fully charged at 14.6v with 20% remaining at 12.8v. which you don't want to drop below.

12v charging system typically operate 13.8-14.2v which means a std 12v charging system cannot overcharge a LiFePO4 battery. cells however can get unbalanced without an internal BMS.

LifePO4 batteries are starting to come with an internal BMS. Earth-X has an internal BMS that self balances cells. Shorai may not claim it but their behavior indicates presences of an internal BMS on some Shorai batteries.

LiFePO4 has an extremely low self discharge. after you charge a LiFePO4 battery to 14.6v ... observe it's discharge ... after sitting overnight battery will drop to 14.1v range, then hold that charge level for months.

if LiFePo4 battery has an internal BMS, voltage will drop to 13.85v range after sitting overnight. there's an internal shunt that bleeds off excess voltage, allowing cells not fully charged to reach full charge. some LiFePO4 battery has external ports allowing use of an intelligent charger that balances each cell.

note there's very little power 14.6v to 13.85v ... 90% of available power occurs 13.3v to 12.8v range ... extremely flat discharge curve

here's Powerlab 8 charging Shoria with balancing leads. Powerlab 8 is currently world's most advanced li-ion charger that you can actually buy.






_cy_ screwed with this post 01-27-2013 at 04:08 AM
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